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PART II. 




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HOW PLANTS BEHAVE: 







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HOW THEY MOVE, CLIMB, EMPLOY INSECTS 

TO WORK FOR THEM, &c. 



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By ASA GRAY. 



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NEW YORK AND CHICAGO: 

IVISON, BLAKE MAN, TAYLOR, AND COMPANY 

1872. 



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Entered according to Act of Congress, in the year 1872, 

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BY ASA GRAY, 

in the Office of the Librarian of Congress, at Washington, 



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Cambridge University Library, 



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University Press : Welch, Bigelow, Sc Co., 

Cambridge. 



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PREFACE 



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HOW PLANTS GROW, the first part of Botany for Young People and 
Common Schools, was written fourteen years ago, in the endeavor to provide a 
book upon Elementary Botany, adapted to the instruction of young people, even 
of children, yet truly presenting, albeit in a simple way, the leading facts, methods, 
and principles of the science as understood by its masters. The book has been 
successful. It will probably enable a young person, under the guidance of a quali- 
fied teacher, to obtain a larger, truer, and worthier knowledge of Botany than 
many grown people could readily find the way to acquire a generation ago. 

That young people, that all students, indeed, should be taught to observe, and 
should study Nature at sight, is a trite remark of the day. But it is only when 
they are using the mind's eye as well, and raising their conceptions to the rela- 
tions and adaptations of things, that they are either learning science or receiv- 
ing the full educational benefit of snch a study as Botany or any other depart- 

^ 

•ment of Natural History. 

There is a study of plants and flowers admirably adapted, while exciting a 
lively curiosity, to stimulate both observatiou and thought, to which I have 
loug wished to introdace pupils of an early age. 
in which I may make the attempt, and may ask young people to consider not 
only 'How Plants Grow/ but How Plants Act, in certain important respects, 
easy to be observed, — everywhere open to observation, but (like other common 
things and common doings) very seldom seen or attended to. This little trea- 
tise, designed to open the way for the young student into this new, and, I trust, 



The time has now arrived 



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PKEFACE 



attractive field, may be regarded as a supplement to the now well-known book, 
the title of which is cited at the beginning of this prefatory note. If my ex23ec- 
tations are fulfilled, it will add some very interesting chapters to the popular 
history of Plant-life. 

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Although written with a view to elementary instruction, and therefore with all 
pi\acticable plainness, the subjects here presented are likely to be as novel, and 
perhaps as interesting, to older as to young readers. 

To those who may wish to pursue such studies further, and to those who will 
notice how much is cut short or omitted (as, for instance, all reference to dis- 
coverei's and to sources of information), I may state that I expect to treat this 
subject in a different Avay, and probably with somewhat of scientific and historical 
fulness, in a new edition of a work intended for advanced students. 



A. a 



Botanic GAr.DEx, Harvard University, 

4 

February 20, 1872. 



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Vignette Title-PagG. — Left-hand side, an Ivy chmbs by rootlets and a Passion-flower 
by tendrils ; right-hand, a Nepenthes by pitcher-bearing tendrils, and a Morning- Glory by 
twining stem : bottom, at the left of the centre, a Ehodochiton, and at the right a Maurandia 
climb by their leafstalks. Bottom, left-hand side, a Green Orchis (Habenaria orbiculata) sends 
up from between a pair of large round leaves a raceme of long-spurred flowers. Two Orchid 
Air-plants at the top, viz., Stanhopea tigrina at the centre, a Phalsenopsis at the right-hand 
corner. Two leaves of Sarracenia rubra, an American Pitcher-plant, rise from near the lower 
right-hand corner ; in front of them is a Sundew, Drosera rotundifolia ; at the centre a Venus's 
Fly-trap, Dionoea muscipula. 



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HOW PLANTS BEHAVE 



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CHAPTER I. 



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HOW PLANTS MOVE, CLIMB, AND TAKE POSITIONS. 

1. Two plants — one of them common in cultivation, and the other rarer, but 
almost as easy to raise — are looked upon as vegetable wonders, namely, the 
Sensitive Plant and Desmodium gyrans. They are striking examples of 

2. Plants that move their leaves freely and rapidly. In the well-known Sensitive 

Plant {Mimosa 2^ndica) the foliage quickly changes its position when touched, 
appearing to shrink away from the hand. Fig. 1 represents 
a piece of stem with two (compound) leaves ; the lower one 
expanded, as it is in sunshine and when untouched : 
upper leaf shows the position which is taken, by quick move- 
ments, when roughly brushed by the hand. It makes three 
movements. First, the numerous leaflets 
bringing their upper faces together and also inclining for- 
wards; then the four branches of the leafstalk, which were 
outspread like the rays of a fan, approach each other; at 
the same time the main leafstalk 
turns downward, bending at its joint 
with the stem. So the leaf (for it is 
all one compound leaf) closes and 
seemingly collapses at the touch. 
In a short time, if left to itself, 
it slowly recovers the former out- 
spreading position, 

3. The second plant, Desmodmm 
gyrans (we have no common name for it), also belongs to the great Pulse Family, 
and flourishes in Avarm climates. It inhabits the warmer parts of India, but is 



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Fig. 1. Sensitive Plant. 



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HOW PLANTS MOVE, CLIMB, 



easy to cultivate in a hot-house, or even in an open garden during the heat of 
summer. The leaves are of only three leaflets (Fig. 2), a large one at the end 
of the leafstalk, accompanied by a pair of small leaflets, one on each side. The 

end leaflet usually moves too slowly to be 
seen, and only as light is given or withdrawn ; 
we have seen it move rather briskly, however, 




upon one occasion, 
active enough. 



The side leaflets are 



Under the temperature of a 
sultry summer's day they may be seen to rise 
and fall by a succession of jerking move- 
ments, not unlike those of the second-hand 
of a clock, but without' much regularity, now 
stopping for some time, then moving briskly, 
always resting for a while in some part of 
their course, commonly at the highest and 

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lowest points, and starting again without ap- 
parent cause, seemingly of their own will. 
The movement is not simply up and down, 
but the end of the moving leaflet sweeps 
more or less of a circuit. It is not set in 
motion by a touch, but begins, goes on, or 
stops of itself. 

4. Whether these movements are of any 
use to these plants is more than we can tell ; 
nor do we very well know how they are ef- 
fected. The attempts that have been made to explain how the motion is brought 
about need not be considered here. However done, it is clear that the leaves 
move hy their oimi act, — in the one case responding to a touch ; in the other 
independently, or, as we say, spontaneously. 

5. Now, truly wonderful as these two plants are, there is nothing really pecu- 
liar about them. By which is meant, not merely that some other plants are 
known to move as freely, though perhaps less rapidly, but that many ordinary 
plants perform similar movements, in one or both of these ways, and that all 
plants possess similar faculties. The hour-hand of the clock moves as really as 
the minute-hand and the second-hand, although the motion of the latter only is 



Pig. 2. Desmodium gyrans. 



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AND TAKE POSITIONS. 



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that is, the different 
is a familiar case of free 



discerned by the eye. Lifeless things may be moved or acted on ; living bemgs 
move and act, — plants less conspicuously, but no less really, than animals. In 
sharing the mysterious gift of life, they share some of its simpler powers. 

6. The Sleep of Plants, as Linnseus fancifully termed it, 
position which leaves and leaflets take at nightfall, 
movement, only the motion is too slow to be seen by the eye. The Sensitive 
Plant is a good instance of this. Its leaves slowly assume the same posture at 
or' before sunset that they rapidly do when disturbed by a touch or jar, and they 
remain so until the light of morning. Most other plants of the Pulse Family 
(the Locusts, for instance), and many of other families, take a very different posi- 
tion by night from that of day. The end-leaflet of Desmodium gyrans hangs 
down as soon as the light of day begins to wane, but rises and turns its upper 
face to the sun again in the morning. 

7. The Turning of Green Shoots to the Light, which we observe when house-plants 

are kept in our windows, and the turning of the upper face of most leaves 
towards the lighted side, are similar cases of slow movement or bending. Many 
people suppose that the green shoot groivs towards the^light, whereas it only bends 
towards it. One has only to notice the behavior of the slender stemlet of a seed- 
ling Radish, or of any similar plant, when set in a window, and see it bending 
towards the lighted side in a few minutes, before it has had time to grow percep- 
tibly, to be convinced that the growth and the bendiiig are different acts. 

8. The contrary Directions of Stem and Root when springing from the seed are of 



this kind. Read the brief account 



graphs 



and 29, and watch the operation in young seedlings. Note how one end of the 
embryo plantlet rises out of the soil and into the light, and, if need be, turns 
quite round to do so, while the other turns from the light and strikes deeper into 
the ground. This shows that it is the plant itself which acts in taking these direc- 
tions, and that these positions are the result of real movements, however slow. 

9. Climbing Plants aff'ord some of the most curious and most varied illustrations 
of the movements which plants perform; and in these it is easy to see what 
the movements are for. The advantage which a plant gains by climbing is, that 
it may thereby rise higher and get a fuller exposure to the light than it could 
with the same amount, of material if it stood independently. Compare the 
amount of wood or other material in a tree with that of any climber which has 
ascended it and made a support of its topmost branches. Plants climb m 
several ways. Some are 



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HOW PLANTS CLIMB. 



10. Root- Climbers. These creep up the face of rocks or walls^ or the trunks of 
trees, their stemSj as they grow, pressing against the support and adhering to it by 
means of numerous rootlets which they throw out : the end of these rootlets com- 
monly flattens out or expands into a small disk or holdfast which adheres to the 
wall or bark, etc. Ivy, that is, true or '^English" Ivy, is a good example of this. 
See the vignette title-page, left-hand side. Our Poison Ivy and the Trumpet 
Creeper climb in the same way. There is, perhaps, no more effectual mode of 
climbing when bare walls or large trunks are the support. In other cases 



11. Twiners, i. e. Twining Plants, 



have an obvious advantage. 



To twine spi- 




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rally round some supporting body is a common mode of climbing. This is 

done by a 

movement 
of the stem 
itself, not 
less re- 
markable in reality than that of the leaflets of the Desmo- 
dium gyrans, just described, and indeed of similar nature. 
The Hop and some Honeysuckles twine Avith the sun. 
Morning Glory, and all the Bindweeds of the Convolvulus 
Family, Beans, and indeed most of the common twiners, 
turn against the sun, that is, from the left to the right 

hand of the observer. -^ - 

12. When a twining stem overtops its support, the 
lengthening shoot is seen thrown over to one side, and 
usually outstretched, as in Fig. 3. One might suppose it 
had fallen over by its weight ; but it is not generally so. 
If turned over, say to the north, when first observed, it will 
probably be found reclining to the south an hour or so 
later, and an hour later again turned northward. That is, 
the end of the stem is sweeping round in a circle continu- 
ally, like the hand of a clock. It keeps on growing as it 
Fig. 3. Morning Glory, twining, rcvolvcs ; but the revolving has nothing to do with the 

growth, and, indeed, is often so rapid that several complete sweeps may be made 
before any increase in length could be observed. The time of revolving varies in 
different species. It also depends upon the weather, being slow or imperceptible 



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HOW PLANTS CLIMB 



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When the free summit of a twmmg 



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when it is cool, and more rapid when it is warmer. Sometimes it stops when 
everything seems favorable, and starts again after a while. The Hop, Bean, and 
Morning Glory are as quick as any. In a sultry day, and when in full vigor, they 
commonly sweep round the circle in less than two hours. They move by night 

as well as by day. 

two feet or more in length, so as to magnify the motion, this is sometimes rapid 

enough to be actually seen in some part of the circuit. 

13. Because twining stems are often twisted more or less, some have supposed 
that the twisting was the cause of the revolving sweep of the free end. If so, the 
stem below would in a day or two be likely to twist itself off. And twiners sel- 
dom twist much when climbing a smooth and even support. To learn how the 
sweeps are made, one has only to mark a line of dots along the upper side of the 
outstretched revolving end of such a stem (say that of the Morning Glory, Fig. 3), 
and to note that when it has moved round a quarter of a circle, these dots will be 
on one side ; when half round, the dots occupy the lower side ; and when the revo- 
lution is completed, they are again on the upper side. That is, the stem revolves 



by bowling itself over to one side, 



is either pulled over or pushed over, or both, 



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by some internal force; which acts in turn all ronnd the stem in the direction in 
which it sweeps ; and so the stem makes its circuits without twisting. 

14. So the sweeping round of the stem is a movement like that wonderful one 
of the leaflets of Desmodium gyrans, just described, only slower. And here we 
see what it is for. The sweeping movement of the stem is the cause of the twin- 

The stem sweeps round that it may reach some neighboring support ; as it 
grows it sweeps a wider and wider space, that is, reaches farther and farther out. 
When it strikes against any solid body, like the stalk of a neighboring plant, it is 
stopped : but the portion beyond the contact is free to move as before ; and, con- 
tinuing to lengthen and to move on, it necessarily winds itself round the support, 
that is, twines. This is the explanation of twining climbers. 

. 15. leaf-Climbers, Some plants climb by their leaves, Mther the blade, or more 
commonly the petiole, hooking or coiling round something within reach. Olema- 
tis or Virgin' s-Bower is a familiar instance. In all the common species of Clema- 
'tis the leaves are compound, and the divisions of the petiole, or at first the young 
leaflets themselves, bend round the stalks or branches of neighboring plants, or 
any supporting object not too large to be grasped, and so ascend. Lophospermtm 
and Maurandia Chandsome flowering; herbs of the gardens), and one or two other 



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HOW PLANTS CLIMB 



plants of the same family, with simple leaves, climb freely in this way, neatly 



coiling their leafstalk round any slender support within reach. 
title-page shows two illustrations of this, in the lower part. 



The vignette 




16. A rather common cviltivated species of 



Nightshade, Solanum jasminoides, is a good 



ex- 



ample of the same kind, and furnishes the 
present illustration, in Fig. 4. It is interesting 
to notice how the leafstalks of this plant which 
have clasped a support grow much stouter and 
firmer than those which have not, becoming 
three or four times as thick as before, — as if 
the need of greater strength and rigidity some- 
how brought it about. 

17. A leaf-climber has this advantage over a 
twiner, that it may reach a given height with 
less amount of substance. Its stem may rise 
straight up, and save much in length over the 
twiner, which has to produce twice or thrice that 
length of stem in reaching the same elevation, on 
account of the coils. 

18. To understand how leaves or leafstalks lay 
hold of a support, we must refer back to the Sen- 
sitive Plant (Paragraph 2) ] its leaves and leafstalks, we know, respond to the 
touch of a foreign body by a movement. So do those of leaf-climbers : only the 
movement by which they clasp the support is very slow and incited only by pro- 
longed contact. If one of these leafstalks be rubbed for some time with a piece 
of wood, it will generally respond to the irritation by curving ; but it will be two 
or three days about it ; and in two or three days more it may straighten itself, 
unless the stick is left in contact with the leafstalk : then it will clasp it perma- 
nently, making one or perhaps two turns around it, and in time it may thicken 
and harden. That the climbing in such cases is the result of a movement, how- 
ever slow, under sensitiveness to touch, is further shown by the behavior of 
tendrils. 

19. Between leaf-climbing and tendril-climbing there is every gradation. In 
Gloriosa, a tropical plant of the Lily Family, the tip of a simple leaf extends 



i'ig. 4. 



Solanum jasminoides, climbing by- 
its leafstalks. 



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HOW PLANTS CLIMB 



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into a slender hook, for laying hold of anything within reach. In Nepenthes (a 

climbing sort of Pitcher-plant, shown on the right-hand side of the vignette title, 

and one leaf in Fig. 5, on a larger scale), the tip of the 

blade grows out into a tendril which acts just as does the 

leafstalk of Fig. 4 and of the other leaf-climbers ; at the 

end of this a pitcher, with a lid to it, is generally formed. 

Of this more is to be said hereafter. 



In that vigorous 



climber, Cohxa, the branching claws and grapples which 
are used to such effect are merely the upper portion of 
a compound leaf changing into tendrils. The tendrils of 
a Pea are similar, but simpler, 

20. Tendril-Climbers are best illustrated by such plants 
as Passion-flowers (see vignette title, on the left, and Fig. 
6) : here the tendril is a simple thread-like shoot, for the 
purpose of cHmbing and nothing else. This is the most 
exquisite, and under many circumstances the most advan- 
tageous, as it is one of the commonest of the contrivances 




for climbing. 



The tendril, as it grows, 



stretches out ^'^- ^- ^'''' "' Nepenthes. 



horizontally, as if in search of a supporting object. More slender than a stem 
or any other sort of stalk, it can thus extend farther at the least expense of 

material. 

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21. In the most perfect tendrils, and notably in the slender Passion-flowers 
(such as the annual Fassiflora gracilis, and the Maple-leaved species, P. acerifolia, 
Fig. 6), opportunities for securing a hold are much increased by the revolving of 
the tendril. It sweeps circuits, like the stem of a twiner, although with less reg- 
ularity, sometimes, however, with greater rapidity. In hot weather these tendrds 
often move through the complete circle in an hour or less, or even so fast that 
the motion of the end of a long tendril may sometimes be distinctly seen in a 
part of its course. The revolving of tendrils is more fitful than that of twining 
stems : they often stop for a while, or move very slowly or irregularly. Some 
tendrils, as we shall soon see, do not revolve at all. 

22. If a tendril does not reach anything, after attaining its full growth and 
remaining for some time outstretched, it then either coils up from the end (as 
seen in the middle tendril of Fig. 6), or else becomes flabby, hangs down in an 
exhausted state, dies, and withers away. 



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HOW PLANTS CLIMB. 






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23. When, however^ the fresh and active 

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tendril comes in contact with a neighboring 
stalk, or any similar support, it hooks or coils 
its end round it ; then, haying secured a hold, 
it shortens by coiling up its whole length, or a 
good part of it. This commonly draws up the 
climbing stem nearer to its support, and makes 
it easier for the younger tendrils above to gain 
their hold. A tendril which has taken hold 
and coiled up usually becomes stouter, rigid, 
and much stronger than it w^as before. One 
which w^ould break with an ounce weight be- 
comes capable of supporting two or three 

pounds. 

24. There is a difference to be noticed be- 
tween the coiling of a free tendril and of one 
which has taken hold. It is plainly shown in 
Fig. 6. The loose tendril coils up, if at all, 
from the end, and in a simple spiral or curl. 
But when attached to a support, both ends be- 
ing fixed, it cannot coil in this way. It has to 
coil in the middle ; and the coiling of one part, 
say from right to left, requires another part to 

Fig. 6. Maple-leaved Passion-flower, with ten- twist aS mucll in the OppOSite direction. So 

drils in yarious states. ^^^ ^^.j ^^^ ^ ^^^^^^ -^ ^^^ middle, half twist- 

ing one way and half the other way, as is shown in the loAver tendril of the figure. 
A longer tendril often has three or four, or even five or six, such breaks, the por- 
tions coiled successively in opposite directions. 

25. Pumpkins, Squashes, and all the Gourd Family furnish excellent examples 
of these actions of tendrils. Their tendrils are like those of Passion-flowers, ex- 

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cept that they are mostly branched or compound, and, like the claws of a bird, 
stretch out in several directions. 





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HOW PLANTS CLIMB. 



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26. There is great variety in the behavior of different tendrils. Those of the 
Grapevine do not make sweeps, but stretch out away from the light, or in the 
direction from which least light comes, — an instinct which is apt to lead them 
to a support, — and the two forks diverge, as if feeling for something to lay hold 
of When they reach anything that can be surrounded, one fork commonly grasps 
from one side, the other from the opposite side, somewhat as an object would be 
grasped by a thumb and finger. 

27. The more branching tendrils of the Virginia Creeper equally turn from the 
light, and therefore towards the wall or trunk, which this climber delights to 
occupy and cover. 
When their tips 
reach the wall thev 
expand into a disk 
or flat plate, w^hich 
adheres firmly to 



the surface. 



This 




particularly adapts 
the Virginia Creeper 
to ascending walls 
or other flat sur- 
faces. The tendrils 
which do not attach 

themselves remain ■^^^- ^' ^i^Si^^i^ Creeper : tendril beginning to form its disks or holdfasts. 8. Older 

branches with full-formed disks. 

slender, and in a 

week or two shrink and wither away. Those that do usually spread their branches 
widely apart, like fingers of an outstretched hand, form their disks and fix them 
fast to the wall ; then they contract more or less into coils, and at length grow 
stronger and more rigid ; so that they last for years, and endure a pretty heavy 
strain without breaking or parting from the wall. It is most interesting to see 
how the strain is divided by these five or six separate attachments, by the coiling 
of each branch to give elasticity, so that the pull shall come upon all at once, and 
to note the strengthening of the whole by the formation of more w^oody fibre. 
The strain is distributed among the branches, and the whole combination is so 
strong that it is rarely torn away by wind or storm. 

28. In revolving tendrils the most wonderful thing to remark is the way in 

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HOW PLANTS CLIMB. 






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which they avoid winding themselves around the stem they belong to. The ac- 
tive tendrils are of course near the top of the stem or branch. The growing 
summit beyond the tendril now seeking a support is often turned over to one side, 
so that the tendril, revolving almost horizontally, has a clear sweep above it. But 
as the growing stem lengthens and rises, the tendril might strike against it and be 

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wound up around it. It never does. If we watch these slender Passion-flowers, 
which show the revolving so well in a sultry day, we may see, with wonder, that 
when a tendril, sweeping horizontally, comes round so that its base nears the 
parent stem rising above it, it stops short, rises" stiffly tipright^ moves on in this 
position until it passes hy the stem, then rapidly comes doion again to the horizon- 
tal position, and moves on so until it again approaches and again avoids the 
impending obstacle ! 

29. Other equally curious illustrations might be given; but these may serve 
the purpose of opening the eyes to what is going on aroimd us, awaken an intel- 
ligent interest, and excite to further observation. They are enough to make it 
clear that the two vegetable prodigies described at the beginning of this chapter, 
surprising as they are, have no peculiar endowments. Climbing plants generally, 
and tendril-climbers especially, exhibit both the free movements of the one, and 
the movement in response to external irritation of the other. The sweeping round 
of tendrils is like the movement of the leaflets of Desmodium gyrans : their coil- 
ing upon contact, and the similar coiling of some leafstalks, are to be compared 
wdth the movement of the leaflets and leafstalks of the Sensitive Plant. 

30. This becomes evident when the motion is quick enough to be seen by the 

F 

eye. It has already been stated that a very long tendril of one of the slender 
Passion-flowers has often been seen to move. Still oftener may it be seen to coil 
up at the tip when gently rubbed. This is also to be seen in the Bur-Cucumber 
(Sicyos), a common weed of the Gourd Family, When, in a sultry summer day, 
M'C gently rub, with a stick or with the finger, the upper end of a vigorous tendril, 
it will respond within half a minute by coiling up so rapidly that the motion may 
be distinctly seen. It will soon straighten, but will coil again if the rubbing is 
repeated. If a stick be left in contact the coiling will be permanent; and a 
downward propagation of the same action is what throws the whole tendril into 
spiral coils. « 



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WHY FLOWERS ENTICE INSECTS TO VISIT THEM. 



19 



CHAPTEE II. 



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HOW PLANTS EMPLOY INSECTS TO WORK FOR THEM, 

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31. Plants supply animals with food. That, we may say, is what they were 
made for. In some cases the whole herbage, in others the fruit, seeds, bulbs, 
tubers, or roots, are fed upon. But vast numbers of insects, and some birds 
(such Is humming-birds), draw nourishment from plants, mainly from their flow- 
ers, without destroying or harming them. By their colors, odors, and nectar, 
blossoms attract insects in great . numbers and variety. 

32. Nectar, the sweet liquid which most flowers produce, is the real attraction : 
bright colors and fragrance are merely advertisements. This sweet liquid is often 
called honey ; but nectar is the proper name for it, as it is not really honey until 
it is made so by the bee. Some insects also take pollen (the powdery matter pro- 
duced in the anthers : see How Plants Grow, paragraph 17), either for their own 
consumption or that of their progeny. That may possibly do the plant some 
harm. But the nectar they consume is of no use to flowers that we know of, 
except it be to entice insects. 

33. So flowers are evidently useful to insects, and most flowers are feeding- 
places for them. Where free lunches are provided some advantage is generally 
expected from the treat : and we are naturally led to inquire, 

34. Why should Flowers entice Insects to visit them? What advantage are they 

likely to derive in return for the food they offer 1 In certain cases the use of in- 
sects to flowers is evident enough. When, in early spring, we see Willow-catkins 
thronged with honey-bees, and notice that their blossoms are of the separated 
sort (How Plants Grow, 205),— those of one tree consisting of stamens only, of 
another tree, of pistils only, — and that the bees flying from tree to tree have their 
bodies well dusted with pollen, we may conclude that the bees are doing useful 
work in carrying pollen from the stamen-bearing flowers that produce it to the 
pistil-bearing flowers that require it in order to set seed (see How Plants Grow, 
16, 196). While feeding from the stamen-bearing catkins, their heads and bodies, 
rubbing against the anthers, get dusted with the pollen. When they fly to a 

L 



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20 



HOW PLANTS EMPLOY INSECTS TO WORK FOR THEM. 



tree with pistil-bearing catkinS; some of this pollen is rubbed npon the stigmas, 
and in consequence its fruit may set and the seeds be perfected. The stamens and 
pistils of Willows being on different trees, and the two sorts of trees very likely 
at a wide distance apart, it is. necessary that the pollen should be carried by insects 
or some other conveyance, if the Willow is to be propagated by seed. 

35. It might have been left to the winds to waft the pollen. It is so in Pine- 
trees, Spruces, and the like. But considering what enormous superabundance of 
pollen these trees produce (even when the two sorts of flowers are on the same 
tree) in order to make sure of the result, one cannot doubt Ihat there is great 
economy in the arrangement by which the busy bees are called upon to do the carry- 
ing. In such instances the insects are probably as useful to the flowers as the 
flowers are to the insects. 

36. Why should perfect Flowers need to attract Insects? Far the larger number of 

flowers are perfect^ that is, are furnished with both stamens and pistils : the sta- 
mens are almost always more numerous than the pistils, and encompass them; 
and each anther contains a thousand or many thousand times more grains of pol- 
len than there are of seeds to be fertilized, and all so near or in such position 
that it appears as if the pollen, or a sufficient quantity of it for the purpose, 
must needs be shed upon the stigmas, either with or without the aid of the wind. 
Yet here insects, in searching the blossoms for food, might be helpful even if not 

needful. 

37. There are plenty of flowers, however, to which insects could seemingly be 
of no use. They have stamens and pistils not only close together, but even in 
contact, — shut up together in some cases, so that some of the pollen cannot fail 
to be shed upon the stigma. Pea-blossoms, and those of most of the Pulse Fam- 
ily are examples of this, having ten anthers closely surrounding one stigma, and 
enclosed by a pair of the petals. And in the Showy Dicentra (or Bleeding-heart, 
as it is popularly called, from the shape and color of the corolla), as in all the 
rest of the Fumitory Family, six anthers are completely enclosed with one stigma, 
three on one side and three on the other, in a cavity just large enough to hold 
them. This cavity is formed by the spoon-shaped summits of the two inner petals, 
which never separate, being united only at their tips : those of the two outer 
and larger petals open and turn back. (See Figs. 9, 10.) One would say that 
such blossoms are purposely and effectually arranged to be fertilized without any 
assistance, and to exclude all interference by insects. Yet they produce nectar 



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WHY PERFECT FLOWEKS NEED TO ATTRACT INSECTS. 



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and are visited by bees. Is their nectar provided only for the good of the bee % 
We might suppose so, until we come to know the remarkable fact that, unless 
visited by insects, they seldom ripen a pod or set a seed. The Showy Dicentra, 
which comes from Japan or JSTorthern China, rarely sets fruit in our gai'dens in 
any case. But the wild species of Corydalis and Fumitory, which have their 

V ■ 

flowers on the same plan, seed freely enough. Yet when the blossoms are kept 
covered with fine gauze, so as to exclude insects, little or no seed is produced. 
Evidently then, for some reason or other, insects sucking their honey are not only 
useful, but needful even to such blossoms. Why they should be needful remains 
to be seen. 






9 



Fig. 9. Flower of Bleeding-heart, Dicentra spectabilis Fig. 10. Same, with the tips of the united inner petals pushed 
to one side. Fig. 11. Tips of the six stamens and pistil, which are exposed in Fig. 10, here separated and dis- 
played , magnified. 



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38. If it be wonderful that such flowers as the last do not well fertilize without 
help, although constructed, as we should say, expressly to do it, equally wonderful 
is it to find blossoms with anthers and stigma placed close together, but with some 
obstacle interposed, as shown on near examination j which looks as if the object 
w^re hoiv not to do it, ' * 

39. Iris-flowers are of this sort. There is a stamen to each of the three stig- 
nias, and close beside it. Behind each stamen and partly overhanging it is a 
petal-like body, peculiar to Iris or Flower-de-Luce : these three bodies, appearing 
like supernumerary petals, are divisions of the style, in a peculiar form, notched 
at the end; under the notch is the stigma, in the form of a thin plate. We 
notice that the stigma is higher than the anther; but that is only a part of the 



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22 



HOW PLANTS EMPLOY INSECTS TO WORK FOR THEM. 



difficulty. The anther and the stigma face away from each other. The anther 
faces outwards and discharges its pollen through two long slits on the outer side 
only. The thin plate or shelf is stigma only on its upper or inner face, which is 
roughened and moistened in the usual way for receiving the pollen : the face 

turned towards the anther cannot receive the 

pollen at all. 

40. A less common flower, the beautiful 

(Figs. 13, 




Arethusa, of our northern 

7 " 



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Fig. 12. Iris-flower cut lengthwise, showing 

one stamen and stigma. 



14), is quite as curiously arranged so as jttst 
not to do of itself what is obviously intended 
to be done. The stamen and the style are 
united into a long and wing-margined col- 
umn; the stigma is a shelf; and the anther, 
which is shaped like a helmet, and is fixed to 
the top of the column by a hinge at the back, 
rests upon this shelf, its front edge at bottom 
projecting slightly over its edge, — just as 

r 

the lid of a chest projects a little over the 
front side, for more convenient lifting. The 

4 

anther holds four soft and loose pellets of 
pollen, which are ready to fall out when the 
anther is uplifted. But here again, only the under side of the shelf is actually 
stigma; the pollen lies imprisoned on the upper surface, and can never. of itself 
reach the lower surface, where alone it can act. 

41. There are hundreds of such cases, differing more or less in the arrange- 
raent, but agreeing in this, that the pollen is placed tantalizingly near the stigma, 
yet where it can never reach it of itself, or can seldom and only accidentally do 
so. Surely, if we had the making of these blossoms, we should have turned the 
shelf under the anther of Arethusa the other side up, and have restored the har- 
mony of that averted couple in Iris by turning the two face to face in place of 

back to back. 

42. The flower of Aristolochia 8ipho, or Pipe-vine of the Southern States (a 
large-leaved woody twiner which is cultivated for arbors), shows the same extra- 
ordinary aversion in a different way. From its shape the blossom is called Dutch- 
man's-pipe : it is a tube curved round on itself, largest at the base, contracted at 



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WHY PERFECT FLOWERS NEED TO ATTRACT INSECTS. 



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the orifice^ and then expanded into a flat border. At the very "bottom of it is a 
short and thick mass, consisting- of a broad stigma, to the ontside of which three 
sets of anthers grow fast : these face away from the stigma, so that none of the 
pollen can fall on it; and the crooked tube of the flower, with a narrow openiug, 
must effectually prevent the wind from giving any aid. What can this meanl 

43. To explain the puzzle which such flowers present, we have to consider that, 
by their bright colors, or odors, or the nectar they offer, ^ — sometimes by all three 
allurements combined, always by the latter, ^ — they attract insects; by whose 
usually rough or bristly heads, or legs, or bodies, pollen may be brushed out of 
the anthers, or caught as it falls, and some of it carried to or dropped upon the 

And we must infer that these blossoms are so constructed and arranged 
on purpose that insects may visit and fertilize them ; and that many species are 
absolutely dependent upon such assistance : for, as they would not set seed, they 
could not permanently exist, except for the insects which they nourish in return 
for such service. So we conclude that honey is the wages paid to insects in 
return for the work they do ; and that the fragrance of flowers and their beautiful 
colors, as well as their honeyed sweets, are not merely for our delight, and for the 
use of the insects they feed, but are of primary use to the plant itself. 

44. In confirmation of this view, it is found that flowers which are fertilized by 
the wind, of which there are numerous sorts, produce neither bright-colored 
corollas, nor fragrance, nor honey. 

45. Now that we know the way of it, nothing is more interesting than to 
notice how particular flowers, each in its own way, are arranged so as to be helped 
by the insects that visit them. Iris-flowers (Fig. 12), for instance, are visited by 
bees. These alight upon the outer and recurving, usually crested or bearded di- 

r 

visions of the flower, down the base of which is the only access to the nectar below. 
When sucking out the nectar with its proboscis, the bee's head is brought down 
beneath the anther ; when raised, it Avill rub against it and brush out some of the 
pollen : this, loosely adhering to its hairy surface, is ready to be deposited upon 
the shelf of stigma above, not when the bee leaves the flower, but when it repeats 
the action. When Arethusa (Figs. 13-15) is visited, the head of the bee enters 
the mouth of the flower : in raising it to leave the flower after extracting the nec- 
tar, the head hits the front edge of the helmet-shaped anther, raises it like a lid, 
and receives one or more of the soft pellets of pollen that fall upon it : on again 
entering the flower and again rising to depart, the pollen-loaded head is first 



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HOW PLANTS EMPLOY INSECTS TO WORK FOR THEM, 



brought. 



brought against the sticky stigma, which occupies all the lower face of the shelf, 
and at the next instant raises the lid to receive another charge of pollen. 

46. Before proceeding further to consider how particular flowers are arranged 
to be helped by some particular sort or class of insects^ and each in some pecu- 
liar way, we should contemplate the remarkable conclusion to which we are 

It seems to be this : - — these flowers are so constructed that the pol- 
len^ however near the stigma, is somehow prevented from reaching it of itself, and 
then honey and other allurements are provided to tempt insects to come and convey 
the pollen to the stigma. And the various contrivances for hindering the pollen 
from reaching the stigma directly are excelled only by those for having it done in 
a roundabout way. So Natvire appears to place obstacles in the way^ and then to 
overcome the difficulty of her own making by calling in the aid of insects ! This 
is blocking the wheels with one hand and lifting the vehicle over the obstruction 
with the other. Or it is as if the wagoner of the fable, w^ho prays Hercules to 
help him out of the mire, had bogged his team merely for the sake of calling upon 
Hercules. This is simply incredible. The explanation of one puzzle has brought 
in its train a greater puzzle still. 

47. The solution of this puzzle is simple enough when once hit upon, although 
it has taken a long time to find it out. It not only makes everything plain as 
respects all these flowers, but also, as a true discovery should, clears up and 
explains a great many things besides. The explanation is, that 

48. Cross-Fertilization is aimed at. The pollen w^as not intended to fertilize that 
same flower, but to be conveyed to some other flower of the same species. So in- 
sects, which had seemed to be needful only when the stamens and pistils are in 
separate flowers, or on separate plants, are quite as needful, — indeed, are more 
needful — where these organs stand side by side in the same blossom. The rea- 
son why crossing is advantageous, and in the long run necessary, is that 

49. Breeding-in-and-in is injurious. Close-fertilization, that is, the fertihzation of 
the seeds by pollen from the same flower, is very close breeding indeed. It is 
the next thing to no fertilization at all in plants, that is, to propagation by buds, 
— which may go on, as we know, for a long time : but it is not probable that any 
species could always continue in that way. Cultivators and stock-breeders are 
obliged to close-breed to keep a particular race of few individuals true and to 
heighten its desirable qualities. But sooner or later (in animals soon), more or 
less wide breeding is necessary to keep up vigor and fertility. Wide-breeding is 



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25 



most 



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naturally secured by the structure itself in plants with separated flowers, 
completely in those which, like Willows, bear stamens and pistils upon different 
trees. And in the majority of plants which have perfect flowers it is commonly 
no less secured by arrangements of various kinds for excluding the pollen from its 
own stigmas, and having it conveyed to those of some other flower of the same 
species. 

50. Comprehending now the full meaning of these curious arrangements, we 
may turn back to some of the flowers already noticed, to observe how exqui- 
sitely they are adapted to the purpose in view, and then advance to new and more 
varied illustrations. 

51. Cross-Fertilization in Iris (Fig. 12). A little nectar is produced in the bot- 
tom of the tube or narrow cup of the blossom. The only access to it is a narrow 

I 

channel leading down the united bases of the six divisions or leaves of the flower. 
Now the three inner of these are upright, with their tips curved inwards, shutting 
off" all access in that quarter. But the three outer and larger divisions recurve 
and afford a convenient landing-place directly before the stamen and the over- 
arching stigma. 



Here the bee alights. 



To reach and suck out the nectar with 
his proboscis will bring the head at least as low as the base of the anther. • On 
raising his head to depart he sweeps with it the whole length of the anther and 
dusts it with the pollen now shedding. A little higher the shelf of stigma is hit, 
but only the outer face of it, which is smooth and does not take the pollen at all. 
Flying to the next blossom, the first thing which the pollen-powdered head of the 
bee strikes is the stigma, but this time on the upper face of the shelf or real sur- 
face of stigma, which takes some of the pollen brought into contact with it, and 
so is fertilized. Sinking lower, the head next brushes the anther downwards in 
entering for the nectar, then upwards in departing, and receives a fresh charge of 

pollen to be deposited upon the shelf of stigma of the next blossom visited, and 
so on. 

52. In Arethusa (40, 45, Figs. 13-15). We have never seen bees or other in- 
sects about this flower ; but it is plain from its structure that it cannot set seed 
without their help. As already described, the bee, or other insect of considerable 



size 



r 

can enter the blossom only in front ; and the large and crested recurving 
petal offers a convenient landing-place. At the bottom of the narrowed cup of 
the flower a little nectar is produced, down to which the insect must reach its 
proboscis. In rising to escape, its head must strike the lower face of the over- 



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26 



HOW PLANTS EMPLOY INSECTS TO WORK FOK THEM, 



hanging shelf, which is stigma, and so sticky that an}^ pollen it may chance to 
have brought would be left adhering there. As the head slips by, it must next 

hit the front edge or visor of the hel- 
met-shaped anther, raise it on its hinge, 
and so allow one or more of the four 
loose pellets of pollen to drop out, or 
be brushed out by the insect's head, to 
which some of the pollen w^ould stick. 
When the next flower is entered noth- 
ing is accomplished ; but on departing, 
as before, any pollen on its head would 

r 

be applied to the sticky shelf of stigma 
overhead, the lid then uplifted, and a 
fresh charge of pollen taken from this 
flower to be given to the next, and 
so on in succession. 

53. It is not unlikely 
that the pellets of pol- 





rig. 13. Flo-wer of Arethusa, entire. Tig. 14. A section 

lengthwise. 




I;' J 



len, as they fall out of the uplifted anther of Arethusa, may some- 
times miss the insect's head, or fail to adhere to it, and so be lost. 
But this plan, or something Hke it, serves the purpose in the por- 
tion of the Orchis Family of which Arethusa is the representative. 
In others of that family the result is made surer by considerably 
different, more economical, and wonderfully curious arrangements, 

— such especially as those * 

54. In Orchises and other plants of that particular tribe of the 
Orchis Family. There is only one true Orchis in this .country, and 
that not common, except northward. And its arrangement for fer- 
tilization is not quite so readily understood as in those Orchises which are named 
by botanists Habenaria, of which we have many species. Some of these are plen- 
tiful, such as the Fringe Orchises, either the purple, white, or yellow species. 
The Greater Green Orchis is not so common, but is taken for the present illustra- 
tion on account of the size of its blossoms. A reduced figure of it, with its two 
large round leaves spreading on the ground, and its spike of flowers rising be- 
tween them on a naked stalk, is in the foreground of the vignette title, and a 
single blossom, of only twice the size of life, is represented in Fig. 1 6. 



Kg. 15. Diagram 
of the anther ami 
stigma of Arethu- 
sa, put in upright 
position. 



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65. The peculiarities are mainly these : 
First, the better to attract certain insects 
and repay them for their service, a sepa- 
rate organ for the nectar — in this in- 
stance a long pouch or honey-tube ^ 
attached to the flower. Then, to econo- 
mize the pollen, the whole of it in each 
cell of the anther is done up in little 
packets or coarser grains, which are tied, 
as it were, to each other by delicate 
elastic threads, and all made fast by 
similar threads to the upper end of a 
central stalk. Finally, to make sure of 
its being taken by the insect and not 
dropped or lost in the carrying, the 
other end of this stalk bears a flat disk, 
commonly button-shaped, the exposed 
face of which is very sticky ; and this is 
placed just where it will be pretty sure 
to be attached to the head or proboscis 
of an insect that comes to drain the 
honey-tube. So that the insect, on ris- 

r 

ing from his meal, will probably carry off 
bodily the whole pollen of that flower 
(or of one of its anther-cells), and be- 
stow it, or some of it, upon the next 
flower or flowers visited. 

66. In this particular species, the front 
petal is, as usual, the insect's landing- 
place. The other petals are more arch- 
ing than the front view- of the flower in 
Fig. 16 represents, and obstruct access 
on all other sides. The long and narrow 
front petal turns downwards and allows 

r 

convenient approach. Underneath hangs 




Fig. 16. Flower of Greater Green Orchis (Habenaria 
orbiculata). 17. Its stamen and stigma more enlarged. 
18. One of the pollen-masses with its stalk and disk, 
equally enlarged. 19. Its disk and a part of the stalk 

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more magnified. 



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HOW PLANTS JMPLOY INSECTS TO WOllK FOK THEM, 



the honey-tube, its mouth opening just behind the base of this petal. Only the 
lower half of the tube, more enlarged and capacious, gets filled with nectar. To 

drain a cup which is about an inch and a half 
deep requires a long proboscis, much lono-er 
than any bee or wasp possesses. Butterflies 
and moths are our only insects capable of do- 




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; and one could predict from a view of 
the flower that the work is done by them. In 

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fact we have hardly a butterfly with proboscis 
long enough to reach the bottom of the cup : 
so we conclude that one of the Sphynxes or 
Night-moths, such as flock around the blos- 
soms of the largest Evening-Primroses at du^k, 
is the proper helpmate of the Greater Green 
Orchis. The Smaller Green Orchis is much 
like the Larger, but with honey-tube hardly an 
Fig. 20. Side view of head of a moth (Sphynx iuch long. This may be drained by many of 

drupiferarum), which has just extracted a -i , , n- 

pair of Orchis pollen-iaasses. ^^ Dutternies. 



Some of these have been 
caught wdth a remarkable body attached to 
their great eyes, one on each eye ; on exam- 
ination this body proved to be quite like that 
rej)resented in Fig. 18, only smaller. This 
body, as we have seen, is the pollen of one 
of the cells of an Orchis anther, with its 
stalk and sticky disk, the latter adhering to 
the insect's eye. How^ did it get there 1 

57. The centre of the flower (as in Fig. 
16) is occupied by the'one large anther, and 
by the concave stigma. The anther is of 
two cells, which taper towards the front of 
the flower and diverge, in this species widely, and the whole space between the 
two diverging horns on the sides and the orifice of the honey-tube below is stigma, 
a broad patch of glutinous surface. At the tip of each horn of the anther, facing 
forwards and partly inwards is the button-shaped, sticky disk. Bring the point 
of a blunt pencil, or the tip of the little finger, or anything of the proper size, 




Fig. 21. Front riew of the same, with the pollen- 
masses in the position they soon take. Both 
figures magnified to the same degree as is the 
Orchis flower in Fig. 16. 



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down into the flower so as to press gently upon these disks for a moment ; then 
withdraw it : the disks will stick fast, and the stalks with the pollen-mass be 
drawn out of the anther. Now the tip of the finger or the pencil is just in 
the position which the head of the large butterfly or moth would occupy when 
its proboscis is thrust deep into the honey-tube. In draining the nectar from 
the tube the insect's head is brought down close to its orifice, its large projecting 
eye on one side or the other, or on both at once, is pressed against the sticky but- 
ton ; and when the moth raises its head and departs, it carries away bodily one 
or both of the pollen-masses. With these the next flowers visited may be ferti- 

lized. 

58. Except by the insect's aid as a carrier, secured by this most elaborate and 
wonderful contrivance, these Orchis flowers could never be fertilized. Close as 
the. pollen is to the stigma, it evidently cannot reach it by any ordinary chance. 
And it w^ould appear as if the obstacles were not eftectually overcome even when 
a moth or butterfly is so ingeniously employed to convey the pollen from one blos- 
som to another, which is plainly what is. intended. For the position of parts is 
such that when the pollen-masses are extracted by the moth's head, they will 

r 

stand pointing upwards and forwards, as shown in Fig. 20. The stalk is too stiff 
to allow them to subside by their own weight. So when the moth alights upon 
the next flower and thrusts its proboscis down its honey-tube, the pollen-masses it 
has brought would hit the anther, quite above the stigma, and effect nothing. 
But all this is accurately provided for. As may be seen by watching the pollen- 
masses when taken upon the point of a pencil, within from ten to thirty seconds 
their stalk turns downward, as if upon a joint between it and the adhering disk, 
bringing them into a position like that represented by a front view in Fig. 21. 
Now the pollen-masses will accurately strike the stigma ! 

59. In some Orchises, and where this adjustment is needful, the pollen-masses 
on the insect's head not only turn downwards but converge inwards, always in the 

* 

way and to the degree necessary for their striking the stigma. In the larger 
Green Orchises, from which the illustrations are drawn, the sticky disk is almost 
parallel with the stalk of the pollen-mass at its lower end, and attached to it by a 
short intermediate joint, as shown in Fig. 18, and more magnified in Fig. 19. It 
is nearly the same in the Yellow and the White Fringed Orchises, which flower 
later in the season. In all these the disks face partly inwards, at considerable 
distance apart, and are stuck to the eye of the butterfly that visits them. In 




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HOW PLANTS EMPLOY INSECTS TO WOBK FOR THEM, 



* * 



others the^ disks are "borne directly upon the end of the stalk, are generally closer 
together, and get applied to the front of the head, or sometimes to the proboscis 
of the insect. 

60. When a pollen-mass, thus carried on the head of an insect, is brought into 
contact with the stigma, some of the pollen will cleave to its glutinous surface 
and be left there, the little threads that bind it to the stalk giving way ; another 
portion will be left upon the stigma of the next flower visited, perhaps on the next 
also, and so nearly all the pollen be turned to good account. Sometimes the ad- 
hesion of the disk to the insect's eye is less strong than the threads that bind the 
frains to the stalk on the one hand, and than the adhesion to the stigma on the 
other. Then the whole pollen-mass is left upon the stigma of that flower, and its 
pollen taken in turn, to be exchanged for that of the next flower ; and so on. In 
any case each blossom will be fertilized by the pollen of some other blossom, 
which is the end in view ; and a more ingenious contrivance for the purpose can- 



not be imagined. 



6 1 . The student should see all these curious things Math his or her own eyes, in 
order fully to comprehend and enjoy them. Once understood in our common wild 
Orchises, it will be equally interesting to find out how it is done, in more or less 
different and varied ways 

, — whether wild ones, such as Ladies' Tresses, Calo23ogon, 



62. In other Orchids 

etc., or in those various and more gorgeous ones, mostly air-plants of tropical re- 
gions, which adorn rich conservatories. Some of these curiously resemble butter- 
flies themselves, — either a swarm of them, as some of the smaller ones in a clus- 
ter on a long light stalk, fluttering with every breath of air ; some are like a large, 
single, gorgeous, orange and spotted butterfly : Oncidkm Papilio, for example 
(Fig. 22), which takes its name from the singular likeness, Pcqnlio being Latin for 
butterfly ; and Phalasnopsis^ a plant of which, greatly reduced in size, is represented 
on the vignette title-page (upper right-hand corner), with large white flowers, 
takes its name from its resemblance to a moth. Can the likeness be a sort of 
decoy to allure the very kinds of insect that are wanted for fertilizing these same 
flowers 1 Sometimes the strange shapes are not' like insects; the flowers of 
Stanho'pea tigrina, for example (figured at the top of the vignette title-page), 
resembhng in color and form rather the head of a cuttle-fish than any known 
insect. 

63. In lady's-SlippeP, or Cypripedium, the plan for securing fertilization is so dif- 



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AND CROSS-FERTILIZE THEIR FLOWERS. 



31 




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ferent from that of any other of the Orchis Family as to need a separate descrip- 
tion, but a very brief one must serve, as we have no figure ready. We refer to our 
wild species ; and first to the 
yellow ones and to the large 
white and pink one, Gypri- 
pedium spectahile, the Showy 
Lady's-Slipper. Unlike other 



Orchids, there are two sta- 
mens : the pollen is powdery, or 
between powdery and pulpy, 
and not very different from 
that of ordinary flowers. As 
it lies on the open anther in a 
broad patch, it somehow gets 
a film like a thin coat of sticky 
varnish. The stigma is large, 
flat, and somewhat trowel- 
shaped, the face turned for- 
wards and downwards : it is 
supported on a stout style, to 
which the anthers have grown 

r 

fast, one on each side. This 
apparatus is placed just within 
the upper part of the sac or 




Fig. 22. Oncidium Papilio. Fig. 23. Comparettia rosea, 

are Epiphytes, or Air-plants, and reduced in size. 



Both 



slipper (rather like a moccason or buskin than a slipper), which gives name to the 
flower. There are three openings into the slipper; a large round one in front, 
and the edges of this are turned in, after the fashion of one sort of mouse-trap ; 
two small ones far back, one on either side, directly under each anther. Flies and 
the like enter by the large front opening, and find a little nectar apparently be- 
dewing the long hairs that grow from the bottom of the slipper, especially well 
back under the overhanging stigma. The mouse-trap arrangement renders it dif- 

r 

ficult for the fly to get out by the way it came in. As it pushes on under the 
stigma it sees light on either side beyond, and in escaping by one or the other of 
these small openings it cannot fail to get a dab of pollen upon its head, as it 
brushes against the film with which the surface is varnished. Flying to the next 



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32 



HOW PLANTS EMPLOY INSECTS TO WOKK FOR THEM, 



blossom and entering asT:)efore, as the insect makes its way onward, it can hardly 
fail to rub the pollen-covered top of its head against the large stigma which forms 
the roof of the passage. The stigma of every other Orchid is smooth and glu- 
tinous. This is merely moist and finely roughened : the roughness^ comes from 
very minute projections, all pointing forwards, so that the surface may be likened 
to that of a wool-card or of a rasp on a very fine scale. So, as the insect passes 
under, the film of pollen is carded or rasped off its head by the stigma and left 
upon it ; and when the fly passes out it takes a fresh load of pollen on its head 
with which to fertilize the next flower. ,.This mode of action we first predicted 
from an inspection of the flower and a simple experiment. It has since been con- 
firmed by repeated observations. The early-flowering and purple Stemless Lady's- 
Slipper differs from the others in having its larger slipper or sac pendent, and 
with a long slit in front, instead of a round open orifice ; the two lips of the slit 
are mostly in contact, but the fly may readily push its way in ; the way of exit 
is more open than in the other species. 

64. In Asclepias or Milkweed, Now and then the rough legs of butterflies and 
bees are found to be encumbered w^ith bodies sticking to them which resemble the 

pollen-masses of Orchids ; but there is always a pair of them, of waxy 
appearance, hanging by a curved stalk from a dark-colored disk, if it 
may be so called, which is not button-shaped. These are the pollen- 
masses of Milkweed, carried off" by insects alighting on the flower to 
suck the nectar from five little cups, and, sticking fast to their legs or 
feet, are so carried from flower to flower. Fig. 24 shows a pair of 
poUen-mlsses them. Milkwccds are like Orchids in this respect only. Their flow- 
of Milkweed, q^h ^yq vcry different and peculiar, not readily to be explained ex- 
cept with the plant itself in hand; but insects are equally necessary to fertilize 

r 

them. 

65. How ordinary blossoms are cross-fertilized by insects passing continually 
from flower to flower will be obvious enough after these explanations. But ob- 
serving eyes will detect many curiotis arrangements in the commonest plants, now 
that the way is pointed out, A few may be described. 

QG^ In Barberry-blossoms there is a remarkable peculiarity. We have learned, in 

* 

the first chapter, that certain plants are endowed with the power of moving some 
part freely in order that they may climb. Barberry-blossoms have a movement 
upon irritation, which has long been familiar as a mere curiosity, but which we 




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83 




now begin to understand the meaning of. It is turned to account in fertiliza- 
tion. The six stamens surround a pistil^ but diverge away from it, as if to be 
sheltered, one under each of the concave or arching petals. There 
they remain unless touched, as with a pin or any other body, at the 
base of the filament on the inside ; then the stamen starts forward 
suddenly, as with a jerk, into an erect position. Not far enough for- 
w^ard, however, for the anthers to hit the stigma ; indeed, the filament 
is not quite long enough for that. Now the anther opens in an un- 
usual way, namely, by trap-doors, one on each side (as shown in Fig, 
25), letting the pollen drop out. Barberry-blossoms are visited by ^^^-25. stamen 
honey-bees and by smaller flying insects ; in the common Barberry the anther^ op^- 

A touch by the proboscis of a bee hoveriuR- un- ^°s ^^ *^^p- 

-, , 1 . floors. 

derneath causes the stamens m turn to spring forward suddenly, and to 
shower the insect plentifully with their pollen. Some of this may be applied im- 
mediately to the button-shaped stigma of that very flower; but some would 
surely be carried to the stigma of the next flowers visited, and so on. In species 
with upright flowers, the pollen will dust the proboscis and head of the bee, or 
of smaller insect crawling to the bottom for the nectar there ; and in entering a 



flowers are hanoino;. 



maa 



67. In Kalmia {American Lmtrel, and equally in the smaller species, namely, 
Sheep Laurel or Lambkill, and in the earlier-flowering Glaucous Laurel of the 
bogs), a mechanical instead of a vital movement is turned to similar account. 
The singular structure of the blossom has long been known; the operation of it 
is only now understood. 

^^ r 

68. This is the plan of it. Ten stamens with slender filaments surround a 
still longer style : the tip of the style is the stigma, which the pollen is somehow 
to reach. But the anthers in the flower-bud lie in as many pouches in the sides 
of the corolla (Fig. 26). When the corolla opens and takes its saucer-shaped 
form, the anthers remain lodged in the pouches, so the filaments are bowed back 
and become so many springs (Figs. 27, 28). If untouched the springs generally 
remain set until the corolla begins to fade : by that time the- filaments lose their 
elasticity and become flabby also. If we jostle them, howevef, by a somewhat 
rude touch when the flower is in fresh condition, so as to liberate the anther, the 
filaments straighten elastically and suddenly, and generally curve over in 
the opposite direction. As they fly back they discharge a quantity of pollen, 

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HOW PLANTS EMPLOY INSECTS TO WORK FOR THEM, 




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Take notice that these anthers do not open by trap-doors, like those of Barberry, 
nor by long slits as in most flowers. As in most of the Heath Family (to which 
Kalmia belongs), they consist of a pair of sacs, side by side, which open by a 
round hole at the top (see Fig. 29). So, when the bowed filament is set free and 
flies forward, the grains of pollen in the anther are projected, like shot from a 
child's pea-shooter. A bit of whalebone, to the end of which two pieces of qnill 
filled with small shot are made fast, is not a bad representation of one of these 
stamens. This really must be a contrivance for discharging pollen at some object. 
If the stigma around which the stamens are marshalled be that object, the target 
is a small one, yet some one or more of the ten shots might hit the mark. But 
the discharges can hardly ever take place at all without the aid of an insect. 
Bees are the insects thus far observed to frequent these flowers ; and it is inter- 
esting to watch the operations of a bumble-bee upon them. The bee, remaining 
on the wing, circles for a moment over each flower, thrusting his proboscis all 
round the ovary at the bottom; in doing this it jostles and lets off* the springs, 
and receives upon the under side of its body and its legs successive charges of 
pollen. Flying to another blossom, it brings its pollen-dusted body against the 
stigma, and, commonly revolving on it as if on a pivot while it sucks the nectar 
in the bottom of the flower-cup, liberates the ten bowed stamens, and receives 
fresh charges of pollen from that flower while fertilizing it with the pollen of the 
preceding one. This account is founded on the observations of Professor Beal, of 
Michigan, who also states that when a cluster of blossoms is covered with fine 
gauze, no stamen gets liberated of itself while fit for action, and no seed sets. 







26 



27 



28 



29 



Figs. 26-29. Flower of American Laurel , Kalmia latifolia. 26. Flower-bud divided lengthwise. 27. 
Open flower. 28. Section of same, lengthwise. 29. A stamen enlarged, discharging pollen from 
the two holes at the top. 






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35 



69. One might doubt whether such movements as those of the stamens of Bar- 
berry ?ind of Kalmia were really intended for the use here assigned to them. 
Bat they serve this purpose, unquestionably, and we can think of no other. Now 
there is a flower of a tropical Orchid, cultivated in some conservatories (named 
Catasetum), in which a movement under irritation (analogous to that of the Bar- 
berry-stamen) and one of elasticity (like that of Kalmia) are combined in one 
apparatus, — one so elaborate and special that nobody can doubt that it is a con- 
trivance for this particular purpose. It cannot well be described here without 
numerous figures and much detail. But the amount of it is, that a sensitiveness 
of two slender and partly crossed arms, which the moth or other large insect must 
hit in reaching the flower-cup, liberates a pollen-mass which is set as a spring, and 
lets it fly like a catapult ; it hits the head of the insect at some distance, disk-end 
foremost, and sticks fast to it, in proper position to be applied to the stigma of the 

next proper flower visited. 

70. Returning to flowers of ordinary structure, and of familiar kinds, two par- 
ticular arrangements for insuring cross-fertilization in perfect flowers must be 
briefly noticed. The commonest is that of 

71. Dicliogamous Flowers. Dichogamy is the name given to the case in which 
the stamens and the stigmas of the same blossom come to perfection at different 
periods. That is, the anthers mature and discharge their pollen in some plants 
before the stigma is ready to receive it, in others only after the stigma has with- 
ered. Either way, the pollen that fertilizes and the stigma that is fertilized can 
never belong to the same blossom. 

72. In the Common Plantain of our dooryards and waysides, Plantago major, and 
in the English Plantain, or Ripple Grass (P. laiiceolata) of the fields, this is famil- 
iarly illustrated. .The style projects from the apex of the closed bud, ready to 
receive pollen from other flowers a day or two before its stamens are hung out 
upon their slender filaments, to furnish pollen for other flowers, — not for their 
own, the stigma of which is by that time dried up. Plantain-flowers, however, 
produce no nectar^ and are neither fragrant nor brightly colored ; so they are not 
visited by insects, but are left to the chance of the conveyance of the pollen by 
the wind. It is the same with many Grasses and Grains, only in reverse order. 
Their anthers hang out on their slender filaments one morning, and the feathery 
stigmas of that blossom not until the nest morning; and the wind is the pollen* 
carrier. 



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36 HOW PLANTS EMPLOY INSECTS TO WORK FOK THEM, 

73. In FigWOrt or ScropMarla, and in many other flowers of which this may 
serve as an example, the work is done with much saving of pollen by calling in 

the aid of insects. Fig. 30 
is an enlarged representa- 
tion of one of the flowers, 
as it appears throughout 
the day of opening. The 
style projects from the 
gorge of the corolla,, pre- 

the stigma just 
over the front edge. The 
stamens are out of sight 
and reach, and not yet 






senting 



32 



SO 81 

Fig. 30. Flower of Scrophularia nodosa, the first day. 31. Inside view of 
it, the front half cutaway. 32. Flower as it appears on the second day. ready: they lie recurvcd 



below, 



as shown in Fig. 



31. A day or two later the flower appears as in Fig. 32 : the style is flabby or 
withering, and the stigma dried up; the stamens have straightened their fila- 
ments, and have brought up the four now opened anthers above the front edge of 
the corolla, where the stigma was the day before. The bottom of the corolla- 
cup contains some nectar. Honey-bees are attracted by it. When they visit a 
flower in the state of Fig. 32, alighting as they do on the front lip, they get the 
chest and legs well dusted with pollen, none of which has acted upon its own 
stigma ; for that was dry and effete before these anthers opened. When the bee 
passes to a freshly expanded flower, such as Fig. 30, the parts covered wdth pol- 
len are sure to be brought against the fre^h and active stigma, which cannot have 
possibly been touched by any pollen of that flower, its anthers being still imma- 
ture and hidden below. 

74. In some other Flowers the pollen is conveyed from an earher to the stigma 
of a later blossom, the anthers maturing and shedding their pollen before the 
stigma is ready to receive any. A beautiful case of the sort, in which a move- 
ment comes conspicuously into play, may be seen in Clerodendron Thompsonice^ a 
climbing shrub from tropical Africa which blooms in our conservatories. Four 
stamens with very long filaments and an equally long and slender style are rolled 
up together in the corolla-bud. When this expands, the stamens straighten out 
nearly in the line of the tube of the corolla, and their anthers open : the style 



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AND CKOSS-FERTILIZE THEIR FLOWERS. 



37 



has bent so far forwards as to point downwards, and the stigma is not yet ready for 
pollen, its two branches being united. So a butterfly, in the act of drawing nectar 
from this flower, will get the under side of its body dusted with pollen, but will 
not come near the reflexed and still immature style. But in a flower a day older, 
the stamens are found to be coiled up (the opposite way from what they were in 
the bud) and turned down out of the way, bringing the anthers nearly where the 
stigma was the day before; w^hile the style has come up to where the stamens 
were the day before, and its stigma with branches outspread is now ready for 



pollen, 



is just in position and condition for being dusted with the pollen which 



the butterfly has received from the anthers of an earlier blossom. 

75. Campanulas and Sabbatias also mature their anthers and shed their pollen 
long before the stigmas open so as to receive ahy ; they, too, are fertilized by in- 
sects carrying pollen from an earlier to a later flower. To understand how it is 
done in each particular case the flowers themselves should be studied in the field 

and garden. . 

76. Dimorphous Flowers, that is, flowers of two kinds as to length or position of 
stamens and pistil, but both sorts perfect, remain to be consiSered. In these the 
difference is only in the stamens and pistil, usually merely in their relative length, 
and very likely to be noticed only by the attentive observer, A good case of this 
may readily be seen 

77. In Houstonia. The com- 
monest species, the little blue- 
eyed Houstonia ccemdea, looks 
up to us from every low mead- 
ow in spring as soon as the turf 

-'ets dry enough 4o set foot 



upon 



In diff*erent patches of 



it, some flowers will show the 
tips of the four stamens slight- 
ly projecting ; as many others 
will show the two 



stigmas 





only. The two kinds are al- 
ways in different patches ; all 
that come from the same seed 



being alike. The sort that shows the tips of the anthers (as in Fig. 33, and with 



Figs. 33, 35. The two sorts of flower of Houstonia caerulea. 34: 
and 36. Same more enlarged, witli corolla divided and laid 
open. 



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HOW PLANTS EMPLOY INSECTS TO WORK FOR THEM 



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flower. 



stigmas. 



So the high anthers are to fertilize the high 



corolla divided and spread open in Fig. 34) has a short style, which brings the 
two stigmas up to near the middle of the tube of the corolla. The sort that 
shows the stigmas projecting (as in Figs. 35 and 36) has the style long enough to 
bring them up just to the place which the anthers occupy in the other flower ; 
but its anthers are placed as low down in the tube as the stigmas are in the first 

The little Partridge Berry of the woods has its flowers of two sorts, on 
the same plan : and among garden flowers it may be seen in Primroses. But it 
is to be noted that this plan occurs only in flowers that are frequented by insects. 

78. In the Houstonia, small insects, feeding by a proboscis, passing from flower 
to flower, take from the high-stamened one (Figs. 33, 34) some pollen upon 'the 
face, as it is brought down close to the orifice of the corolla when the proboscis 
is thrust to the bottom for the nectar there. When the insect passes to another 
flower of the same sort, it merely gets its face smeared with a little more pollen. 
But when it visits a long-styled flower (such as Figs. 35, 36) and brings its head 
down to the orifice, it will apply some of this pollen to the stigmas, which are 
exactly in the position to receive it. 

How about the low stamens and low stigmas, when the insect flies from 
a flower of the second sort to one of the first, as it is quite as likely to do 1 
Why, the insect's proboscis, as it explores that flower, gets dusted with the pollen 
of the low anthers, and this pollen is neatly carried and applied to the similarly 
placed stigma of the other kind of flower. So much for dimorphous flowers. 
There are even 

w 

79. TrimorphOUS FlowerSj that is, perfect flowers of three sorts arranged to co- 
operate in this^ way. One case at least was discovered by the most sagacious 
investigator of this whole class of subjects (Mr. Darwin), in a kind of Loosestrife 
{Lythrum Salicaria), and there is something nearly like it in another bog plant of 

3a verticillata. There are three lengths of style and 
three lengths of stamens, two of the latter in each sort of flower, the stamens 

Bees suck the flowers of this Loosestrife. In doing so, the 
longest stamens rub their pollen against the lower and hinder part of the body 
and the hind legs; the middle-length stamens, between the front pair of legs; 
the shortest stamens, against the proboscis and chin. When they fly to other 
flowers, the very parts that are dusted with long-stamen pollen rub against the 
stigma of the long style; those dusted with that of middle-length stamens, 
against the stigma of middle-length style ; those with that of short stamens, against 



Nes 



being in two sets. 






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AND CROSS-FERTILIZE THEIR FLOWERS. 



39 



A 



the stigma of the shortest style, — each to each. Not only is the pollen, through 
such wonderful arrangements, so distributed as to secure cross-fertilization, but 
the end is further secured by a 

80. Preference of Stigma for Pollen of other Flowers than its own. In dimorphous 

L 

and trimorphous flowers, such as have just been described, it has been ascertained 
that if pollen is placed upon the stigma of the same blossom, or even on that of 
another blossom of the same sort, it takes little or no effect. There are cases 

r 



where the stigma gets naturally covered with its own-flower pollen withou-t set- 



ting seed, but when touched with the pollen of another flower it seeds perfectly. 
This explains, at length, the remarkable thing (described in paragraph 37) that 
the blossoms of Peas, Beans, and of Dicentra or Bleeding-heart and the like, 
generally set little or no seed when insects are excluded, although the parts are 
so disposed that the stigma must be dusted by the pollen of the stamens enclosed 
with it. Why even such flowers need the aid of insects is now clear. This pref- 
erence of pollen for other than its own blossom, however, is strictly 

81. Within tlie limits of the Species. The pollen which is conveyed to the stigma 
of a different species is inactive and without result, in all but species that are 
pretty nearly related, and in many of these. Apple-blossom pollen, for instance, 
does not fertilize pear-blossoms, and vice versa. Cross-breeding among flowers 
of the same species is the rule, — among different species the exception. It may 
be done, however, to a certain extent, but always with more difficulty ; it rarely 



occurs in nature left to itself. 



Bvb 



to it gardeners and florists greatly diversify certain flowers and fruits ; for the new 
sorts produced inherit from both parents \ the cultivator aims at originating and 

J ■ 

preserving those that combine the most desirable qualities of both parents. 



Advanta 



The greater number of species, and far the 



greater number of those that are visited by insects, are perfect, that is, with sta- 
mens and pistil in the same blossom. Yet separated flowers would seem best for 
the end in view, cross-fertilization in them taking place of necessity. But, with 
insects to assist, it is better, that is, more economical, to have perfect flowers ; 
for, while the crossing is equally secured, both flowers produce seed. '* The econ- 
omy of Nature " of which we read is something more than a figure of speech. 

83. The reciprocity of flower and flower, and of insects and flowers, is some- 
thing admirable. Insects pay liberal wages for the food which flowers provide for 



them. 



Watts 



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HOW PLANTS EMPLOY INSECTS TO WORK FOR THEM. 



to the bee visiting the flower as a model of industry. With a slight change of a 
couplet; adapting it to our present knowledge and to the lesson of mutual help- 
fulness, we may read : — 

How dotli the little busy bee 
Improve each shining hour, 

■ 

While gathering honey day by day, 
To fertihze each flower. 

84. Such are the principal modes, thus far known (and when these are under- 
stood watchful eyes may discover other equally curious cases), in which flowers 
are prevented from breeding in and in, either wholly or to such extent as 
to keep up the vigor of the species. Such are some of the ways in which 
flowers are adapted to insects, and no doubt insects to flowers, for this end. 
Plants, destitute of the locomotion and volition which animals, at least the hiQ-her 
animals, enjoy, have the lack made up to them in these subtle and very various 
contrivances, by which the volition and locomotion of insects are made to serve 
them, even to secure their very existence. For, to say that these plants could 
continue to flourish without such aid is tantamount to saying that these multi- 
farious, elaborate, and exquisite arrangements are superfluous, — which is past all 
belief. 

85. It is equally past belief that they are undesigned or accidental. No one 
has been able to describe them except in language which assumes that they are 
contrivances, cidaptcitions for particular purposes, and the like; and where many of 
them are best described they are said to ^' transcend in an incomparable degree the 
contrivances and adaptations which the most fertile imagination of the most imag- 
inative man could suggest, with unlimited time at his disposal." Now, no matter 
whether or not the flowers themselves with all these structures have been 
perfected step by step, through no matter how long a series of natural stages, 
— if these structures and their operations, which so strike the mind of the philos- 
opher no less than of the common observer that he cannot avoid calling them 
contrivances, do not argue intention, what stronger evidence of intention in Na- 
ture can there anywhere possibly be % If they do, such evidences are countless, 
and almost every blossom brings distinct testimony to the existence and provi- 
dence of a Designer and Ordainer, without whom, we may well believe, not merely 
a sparrow, not even a grain of pollen, may fall. 



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HOW CERTAIN PLANTS CAPTURE INSECTS 



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CHAPTER III. 



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HOW CERTAIN PLANTS CAPTURE INSECTS, 



86. This is not a common habit of plants. Insects are fed and allowed to depart 
imharmed. When captures are made they must sometimes be pui^ely accidental 
and meaningless ; as in those species of Silene called Catch-fly, because small flies 
and other weak insects, sticking fast to a clammy exudation of the calyxes in 
some species, of a part of the stem in others, are unable to extricate themselves 
and so perish. But in certain cases insects are caught in ways so remarkable that 
we cannot avoid regarding them as contrivances, as genuine flytraps. 

87. Flower-Flytraps are certainly to be found in some plants of the Orchis 
Family. One instance is that of Gypripedium or Lady's-Slipper, which, being a 
contrivance for cross-fertilization, is described in the foregoing chapter (paragraph 
62). Here the insect is entrapped for the purpose of securing its services; 
and the detention is only temporary. If it did not 
escape from one flower to enter into another, the 
whole purpose of the contrivance would be defeated. 

Not so, however, in 

88. leaf-Flytraps. These all take the insect's life, 
— whether with intent or not it may be difiicult 
to make out. The commonest and the most ambig- 
uous leaf-flytraps are 

89. Such as Pitchers, of which those of our Sarra- 
cenia or Sidesaddle-flower are most familiar. Fig. 37 
represents one leaf, and a section of another, of the 
species most common in our bogs, especially at the 
North ; and the vignette title-page, at bottom on 
the right hand, shows the longer and more tubular 
pitchers of another species of the Southern States. 



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a common yellow-flowered species from 




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Virginia southward, has them so very long and 



Fig. 37- Leaf of the common Sarra- 
cenia purpurea, and one cut across. 



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HOW CERTAIK PLANTS CAPTURE INSECTS. 






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narrow, that they are popularly named TriimpeU. 



In these pitchers or tubes 
water is generally found, sometimes caught from rain, but in other cases evi- 
dently furnished by the plant, the pitcher being so constructed that water can- 
not rain in : this water abounds with drowned insects, commonly in all stages of 
decay. One would suppose that insects which have crawled into the pitcher 
might as readily crawl out j but they do not, and closer examination shows that 
escaping is not as easy as entering. In most pitchers of this sort there are sharp 
and stiff hairs within, all pointing downward, which offer considerable obstruction 
to returning, but none to entering. 



Why 



round need to catch 



water in pitchers, or to secrete it there, is a mj^tery, imless it is wanted to drown 

flies in. And what they gain from a solution of dead flies is equally hard to 

guess, unless this acts as a liquid manure. 

91. Into such pitchers as the common one represented in Fig. 37 rain may 

fall ; but not readily into such as those of the vignette title already referred to, — 

not at all into those of the Parrot headed species, S. psit- 
tacina of the Southern States, for the inflated lid or cover 
-arches over the mouth of the pitcher completely. This 
is even more strikingly so in Darlingtonia, the curious 
Californian Pitchei-^plant lately made known and culti- 
vated : in this the contracted entrance to the pitcher is 
concealed under the hood and looks downward instead of 
upward ; and even the small chance of any rain entering 
by aid of the wind is, as it were, guarded against by a 
curious appendage, resembling the foi^ked tail of some 
fish, which hangs over the front. Any water found in 
this pitcher must come from the plant itself. So it also 
must in the combined 

92. Pitcher and Tendril of Nepenthes. These Pitcher- 

plants are woody climbers, natives of the Indian Archi- 
pelago, and not rarely cultivated in hot-houses, as a curi- 




rig. 38. Leaf-tendril and 
pitcher of Nepenthes. 



osity. 



One is shown on the vignette title, right-hand 



side, and their way of climbing is mentioned in the foregoing chapter (19). Some 
leaves lengthen the tip into the tendril only ; some of the lower bear a pitcher 
only; but the best developed leaves have both, — the tendril for climbing, the 



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HOW CERTAIN PLANTS CAPTURE INSECTS 



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pitcher one can hardly say for what purpose. The pitcher is tightly closed by a 
neatly fitting lid when young ; and in strong and healthy plants there is com- 
monly a little water in it, which could not possibly have been introduced from 
without. . After they are fully grown the lid opens by a hinge ; then a little water 
might be supposed to rain in. In the humid sultry climates they inhabit it prob- 
abfy does so freely, and the leaves are found partly filled wath dead flies, as m 

our wild Pitcher-plants. 

93. The drowning of insects in plant-pitchers is of course an accidental occur- 
rence, and any supposed advantage of this to the plant may be altogether fanci- 
ful. But we cannot deny that the supply of liquid manure may be useful. - Be- 
fore concluding that they are of no account, it may be well to contemplate other 

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sorts of leaf-flytraps. 

94. Sundew as a Fly-catclier. AH species of Sundew (Drosera) have their leaves, 
and some their stalks also, beset with bristles tipped with a gland from which 
oozes a drop of clear but very glutinous liquid, making the plant appear as if 
studded with dew-drops. These remain, ghstening in the sun, long after dew- 
drops would have been dissipated. Small flies, gnats, and such-like insects, seem- 
ingly enticed by the glittering drops, stick fast upon them and perish by starva- 
tion one would suppose without any benefit whatever to the plant. But in the 
broad-leaved wild species of our bogs, such as the common Round-leaved Sundew 
(fio-ured, much reduced in size, at the foot of the vignette title, toward the right), 
the upper face and edges of the blade of the leaf bear stronger bristles, tipped 
with a larger glutinous drop, and the whole forms what we must allow to be a 

veritable fly-trap. 

95. For, when a small fly alights on the upper face, and is held by some of 
the glutinous drops long enough for the leaf to act, the surrounding bristles 
slowly bend inwards so as to bring their glutinous tips also against the body of 
the insect, adding, one by one, to the bonds, and rendering captivity and death cer- 
tain. This movement of the bristles must be of the same nature as that by 
which tendrils and some leafstalks bend or coil. It is much too slow to be visible 
except in the result, w-hich takes a day or two to be completed. Here, then, is a 
contrivance for catching flies, a most elaborate one, in action slow but sure. And 
the diff"erent species of Sundew offer all gradations between those with merely scat- 
tered and motionless dewy-tipped bristles, to which flies may chance to stick, and 
this more complex arrangement, which we cannot avoid regarding as intended for 



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HOW CEKTAIN PLANTS CAPTURE INSECTS. 



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%-catching. Moreover, in one of our species with longer leaves (D. longifolia) 
the blade of the leaf itself incurves (as an intelligent lady has observed), so as to 
fold round its victim ! 

96. Another and a most practised observer, whose observations are not yet pub- 
lished, declares that the leaves of the common Round-leaved Sundew act differ- 
ently when different objects are placed upon them. For instance, if a particle of 
raw meat be substituted for the living fly, the bristles will close upon it in the 
same manner; but to a particle of chalk or wood they remain nearly indifferent. 
If any doubt should still remain whether the fly-catching in Sundews is acciden- 
tal or intentional, — in other words, whether the leaf is so constructed and ar- 
ranged in order that it may capture flies, — the doubt may perhaps disappear 
upon the contemplation of another and even more extraordinary plant of the 
same family with the Sundew^, namely, 

97. VemiS'S Flytrap, or Dionsea muscipula. This plant aboimds in the low savan- 



Wilmi 



It is not 



very difficult to cultivate, at least for a time, and it is kept in many choice con- 
servatories as a vegetable wonder. 

98. The trap is the end of the leaf (see Figs. 39, 
40). It is somewhat like the leaf of Sundew, only 
larger, about an inch in diameter, with bristles still 
stouter, but only round the margin, like a fringe, and 
no clammy liquid or gland at their tips. The leaf 
folds on itself as if hinged at the midrib. Three 
more delicate bristles are seen on the face upon close 
inspection. When these are touched by the finger or 
the point of a pencil, the open trap shuts with a 
quick motion, and after a considerable interval it 
reopens. When a fly or other insect alights on the 
surface and brushes against these sensitive bristles, 
the trap closes promptly, generally imprisoning the 
intruder. It closes at first with the sides convex and 
the bristles crossing each other like the fingers of in- 

Fig. 39. Leaves of Dionsea or Ve- , , , , , ^ ^^ ^ \^ o . i . 

niis's Flytrap, the trap of the tcrlockcd hauds or the teeth of a steel-trap, as m the 

larger one wide open. gi^^ f^g^^^g ^f pj^^ 39^ g^^ ^^^^ ^^^ ^j^^^ ^^ ^^^ 

trap flatten down and press firmly upon the victim ; and it now requires a very 




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HOW CERTAIN PLANTS CAPTURE INSECTS 



45 



considerable force to open the trap. If nothing is caught the trap presently^ 
reopens of itself and is ready for another attempt. When a fly or any similar 
insect is captured it is retained until it perishes, — is killed, indeed, and con- 
sumed ■ after which it opens for another capture. But after the first or second it 
acts slu^-^ishly and feebly, it ages and hardens, at length loses its sensibility, and 

slowly decays. - 

99. It cannot be supposed that plants, like boys, catch flies for pastime or in 

objectless wantonness. Living beings though they are, yet they are not of a suf- 
ficiently high order for that. It is equally incredible that such an exquisite 
apparatus as this should be purposeless. And in the present case the evidence of 
the purpose and of the meaning of the strange action is wellnigh complete. 
The face of this hving trap is thickly sprinkled with glands immersed in its tex- 
ture, of elaborate structure under the microscope, but large enough to be clearly 
discerned with a hand lens ; these glands, soon after an insect is closed upon, give 
out a saliva-like liquid, which moistens the insect, and in a short time (within a 
week or two) dissolves all its soft parts, — digests them, we must believe ; and the 
liquid, with the animal matter it has dissolved, is re-absorbed into the leaf ! We 
are forced to conclude that, in addition to the ordinary faculties and function of 
a vegetable, this plant is really carnivorous. 

100. That, w^hile all plants are food for animals, some few should, in turn and 
to some extent, feed upon them, will appear more credible wheil it is considered 
that whole tribes of plants of the lowest grade (Mould-Fungi and the like) habit- 
ually feed upon living plants and living animals, or upon their juices when dead. 
An account of them would make a volume of itself, and an interesting one. But 
all goes to show that the instances of extraordinary behavior which have been 



* 



* Ellis, who first described the Dionma in full, and gave it this name, noticed the liquid secretion and 
the glands that produce it, but thought that it was given out while the trap was open and as a lure to 
insects: he expressed his belief that the leaves caught insects for the purpose of nutrition. Linn^us 
appears to have doubted this ; he omitted all account of the fluid, and gave a more humane, but incor- 
rect, version of the plant's behavior, stating that the trap holds the insect only while it struggles, but 
releases it on becoming quiet: and this statement has been commonly adopted. Elliott merely copied 
the description by Linnaius. The Rev. Dr. M. A. Curtis of North Carolina (just deceased) gave a 
more correct account about thirty years ago. Recently Mr. William M. Canby of Delaware has pub- 
lished some veiy interesting observations and experiments; which show that the liquid is a sort of gas- 
tric juice, exuded after the capture. He also fed the leaves with morsels of raw beef, and found that 
these in most instances were mainly dissolved in the juice, which then disappeared, evidently by ab- 
sorption. Similar observations and experiments made by Mr. Darwin are still unpublished. 



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HOW CERTAIN PLANTS CAPTURE INSECTS 



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recounted in these chapters are not mere prodigies, wholly out of the general 
order of Nature, but belong to the order of Nature, and indeed are hardly dif- 
ferent in kind from, or really more wonderful than, the doings of many of the 
commonest plants, which, until our special attention is called to them, ordinarily 
pass unregarded- 



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